Propylene-based polymers are generally inexpensive, and exhibit characteristic properties including transparency, mechanical strength, heat resistance, surface gloss, chemical resistance, oil resistance, rigidity, flex clacking resistance, etc., for which they thus have a wide range of uses as industrial materials, food packaging materials, cosmetic packaging materials, drug packaging materials, and the like.
As mentioned above, propylene-based polymers exhibit characteristics such as rigidity, impact resistance, etc., and are thus widely used in various production industries including automobiles, consumer electric goods, miscellaneous goods, and the like. Recently, producers are investigating the prospect of making products thinner in order to render them more light-weight and lower their cost, while increasing the surface strength in order to prevent damage to the surface thereof. That is, demand is increasing for propylene-based polymers which have high rigidity, high surface hardness and excellent impact resistance. Also, demand has continued to increase for a higher level of physical properties and workability, and particularly desired are the maintaining of the rigidity and strength at high temperatures, durability, and the improvement of the moldability of large-size moldings.
Regarding high rigidity and improved transparency and surface gloss of propylene-based polymers, there have been conventionally known methods which employ fillers such as I.sub.a and II.sub.a group metal salts of monocarboxylic acids (for example, sodium benzoate), III-IV group metal salts of dicarboxylic acids (for example, adipic acid) and aliphatic dicarboxylic acids (for example, aluminum adipate), dibenzylidene sorbitol derivatives, talc and the like, as nucleating agents (Japanese Examined Patent Publication (KOKOKU) No. 39-1809, Japanese Unexamined Patent Publication (KOKAI) No. 60-139731, etc.), and methods which create a wide distribution of the molecular weight of propylene-based polymers (Japanese Unexamined Patent Publication (KOKAI) Nos. 56-2307, 59-172507, and 62-195007, etc.).
However, although use of these nucleating agents results in improvement in the aforementioned physical properties, it cannot be said that they are necessarily sufficient for all uses.
Consequently, it has been desired to obtain propylene-based polymers suitable as materials for automobiles, consumer electric goods and packaging materials, which have excellent mechanical strength including impact resistance, rigidity, etc. as well as surface hardness and heat resistance, at the same time lowering the density of the products to render them more thin by reducing the amount of fillers such as talc and the like.
Furthermore, efforts are continuing to improve the stereoregularity (isotacticity) of propylene-based polymers, widen their molecular weight distribution, increase their strength and durability which depend on the molecular weight distribution, and improve the moldability in extrusion molding, blow molding and the like.
Of these efforts, the development particularly of catalysts with high activity and producing high isotacticity are recently being ardently studied. All are catalyst systems comprising a solid catalyst component containing magnesium, titanium, a halogen and an electron-donating compound as essential components, with an organoaluminum and another electron-donating compound, and examples thereof are disclosed in Japanese Unexamined Patent Publication (KOKAI) Nos. 57-63310, 58-32604, 58-83006, 59-206408, 59-219311, 60-130607, 61-209207, 61-211309, 62-72702, 62-104811, 62-11705, 63-199703, 63-264609, 1-126306, 1-311106, 3-62805, 3-70710, 4-103604, 4-114009 and 4-202505.
The present inventors have also made recent disclosures in this regard in Japanese Unexamined Patent Publication (KOKAI) Nos. 4-43407, 4-149217, 4-178406, 4-180903, 4-185613, 4-198202, 4-198204, 5-9209 and 5-287019.
The propylene-based polymers disclosed in the preceding publications have a xylene-extraction insoluble portion of less than 99% and an isotactic pentad ratio (mmmm) of methyl groups in the polypropylene of at most around 93-98%, as measured by .sup.13 C nuclear magnetic resonance spectroscopy (hereunder abbreviated to .sup.13 C-NMR), and thus there have been limits to the improvement in the various physical properties such as rigidity and heat resistance.